The subject matter disclosed herein relates to gas furnaces and in particular to gas furnaces having an inshot burner with a flame retention insert.
Gas fired appliances, such as residential and light commercial heating furnaces, often use a particular type of gas burner commonly referred to as an inshot burner. In this type of burner, fuel gas under pressure passes through a central port disposed at the inlet of a burner venturi. Atmospheric air is drawn into the burner and mixes with the fuel gas as it passes through the burner. In some constructions, a burner head insert, also referred to as a flame retention insert, made of compressed sintered or powdered metal is mounted in the outlet end of the burner tube. In operation, as gas is injected into the inlet end of the burner, it entrains air into the burner. This primary air/gas mix flows through the burner to the flame retention insert. The primary air/gas mix passes through outlet openings defined by the insert and burns as it exits the insert forming a flame projecting downstream from the burner head insert. Secondary air flows around the outside of the venturi tube and is entrained in the burning mixture downstream of the insert in order to provide additional air to complete the combustion process.
Conventional inshot burner designs sometimes provide less than desired performance for ignition, flame stability, noise and combustion efficiency. Ignition problems can arise when the combustion process is not anchored to the retention insert. For example, if the velocity of the primary air/gas flow from the insert is greater than the flame speed, the flame may lift off from the burner insert, i.e. the flame begins to burn at a location spaced from the outer face of the flame retention insert. Flame liftoff contributes to noise associated with the operation of inshot burners. Under other circumstances, the velocity of the air/gas mixture may be too slow when compared to the flame speed. When this occurs, the flame may flashback. Flashback is the burning of the gas within the burner itself. This condition can cause overheating and reduce the life expectancy of the burner.
Flame retention or burner head inserts have been provided in an attempt to achieve better flame stability and reduction of noise. Some flame retention inserts provide an inner flow passage and a plurality of secondary openings having smaller diameters arranged circularly around the central insert. While such flame retention inserts are helpful in addressing the problems discussed hereinabove, they may not adequately address the problem of flashback. Further, as it has become desirable to have smaller furnaces, the burner and flame retention inserts have become shorter in length. This decrease may result in less desirable performance in terms of combustion efficiency since the fuel and air streams have less flow length to mix prior to combustion.
Accordingly, while existing gas furnaces are suitable for their intended purposes, improvements may be made in improving the performance of the combustion process by providing a burner insert that stabilizes the combustion flame, increases the mixing of fuel and air and also decreases the potential for flashback.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.